1. Field of the Invention
The present invention relates to a pressure-sensitive adhesive sheet with release liner comprising a release liner on a pressure-sensitive adhesive layer; and more particularly to a pressure-sensitive adhesive sheet with release liner, which is excellent in operability when releasing the release liner from the pressure-sensitive adhesive sheet and also in recyclability of the release liner. The present invention also relates to a release liner for a pressure-sensitive adhesive sheet, which is excellent in the operability of its release from the pressure-sensitive adhesive sheet as well as in recyclability.
The present application is filed claiming the benefit of the priority based upon Japanese Patent Application No. 2006-256846 filed on Sep. 22, 2006, the entirety of which is incorporated herein by reference.
2. Description of the Related Art
As a release liner for a pressure-sensitive adhesive (PSA) sheet, there has been known a release liner formed of a substrate having a polyethylene (PE) film laminated on a paper core member (release paper). Recently, for the purpose of facilitating air bubble exclusion at the time of PSA sheet attachment or the like, there has been developed a PSA sheet with release liner constructed in a way that an uneven structure formed on a surface of the release liner is transferred to the surface of the PSA layer. As related art documents on this type of technology, Japanese Patent Application Publication Nos. 2004-506777 and 2006-028416 are available. A release liner formed of a PE film laminated on a paper core member is preferably applicable as a release liner having an uneven structure on a surface thereof. For instance, an example in Japanese Patent Application Publication No. 2004-506777 (paragraph 0043) uses a release liner including a paper core member coated with PE on both surfaces thereof.
A release liner (hereinafter, occasionally referred to simply as a “liner”) having a PE layer on a surface of a paper core member in this manner generally has advantages connected with the nature of paper, which are that the liner is separated (released) from the PSA sheet with high operability and that the operability is not so greatly influenced by temperature. However, a liner of such a structure cannot be separated into paper and resin (PE) after use (i.e., after being released from the PSA sheet) and thus is not recyclable. In the case of a liner using paper, the liner itself or the PSA sheet including the liner tends to be undulating due to the surface roughness of the paper grain. This spoils the external appearance of the liner.
There has also been offered a liner with no paper core member. For example, Japanese Patent Application Publication No. 2004-506777, paragraph 0022, describes a liner with PE having silicone release coating covering (laminated on) the surface of polyethylene terephthalate (PET), a liner formed of cast polypropylene film having silicone release coating, and the like.
Polyolefins such as polyethylene, and polyethylene terephthalate are different types of resin. For the purpose of further improving recyclability, more preferable is a liner which is recyclable as a polyolefin material not containing a different type of resin (PET, etc.). For example, in terms of recyclability, a liner formed of a single-layer of polypropylene-based resin (i.e., not laminated on a different type of resin) is preferable.
However, a liner formed of a synthetic resin (especially, a single layer of thermoplastic resin), as compared with a liner having a paper core member, is more likely to be influenced by the environmental temperature in terms of operability when the liner is released from the PSA sheet. For this reason, for example, even release conditions (release posture, release speed, release force, etc.) that realize a smooth release of a liner from a PSA sheet in the environment of 23° C. may not consistently realize a smooth release at a higher temperature exceeding 30° C. (e.g., about 35° C.). This may lead to such as a decrease in the operability. Especially, in a PSA sheet attachment process carried out in such a way that while the liner is being released from the PSA sheet, the PSA sheet is simultaneously being attached to an adherend, there may occur problems such as the liner getting stuck (jammed) unless the smooth release of the liner is maintained.